擅长:python、mysql、java
<p>根据官方文件:</p>
<blockquote>
<p>A DocumentSnapshot contains data read from a document in your Cloud
Firestore database. The data can be extracted with the getData() or
get(String) methods.</p>
<p>If the DocumentSnapshot points to a non-existing document, getData()
and its corresponding methods will return null. You can always
explicitly check for a document's existence by calling exists().</p>
</blockquote>